1. Technical Field
The present invention relates to integrated circuits. In particular, the present invention relates to a method and apparatus for soft error detection in non-data flow (control) circuits.
2. Description of Related Art
Today, a widespread and growing use of semiconductor chips is present in every aspect of daily life. Chips are no longer found just in TVs, VCRs and CD players. Increasingly, chips are replacing relays and mechanical systems that we depend upon to function continuously, twenty-four hours a day. In some cases, these chips are exposed to harsh environments. As such, a major concern in the semiconductor industry today is signal integrity. As minimum layout dimensions continue to shrink, signal integrity becomes harder to maintain. Multiple causes and effects are present that impact signal integrity. One cause that is having an increased impact on Very Large Scale Integration (VLSI) technologies is “soft errors.”
Soft errors, also sometimes referred to as transient errors or single event errors (SEE) or single event upsets (SEU), are errors that are due to temporary conditions of use and the environment. As such, soft errors occur in a statistically unpredictable fashion. If a chip is susceptible to these errors it could fail at any time. In cases of applications that require a high level of reliability, such as high-end computing, monetary transactions and secure network systems, soft error failures can be devastating.
Typical causes of soft errors are ground bounce, radiation and crosstalk. Soft errors can be categorized into two kinds of soft errors, chip-level and system-level. Chip-level soft errors are errors that typically occur when the radioactive atoms in the chip's material decay and release alpha particles into the chip. However, depending on usage, radiation from external sources can have the same effect. Because an alpha particle contains a positive charge and kinetic energy, the particle can hit a memory cell and cause the cell to change state to a different value. The atomic reaction is so tiny that it does not damage the actual structure of the chip. System-level soft errors are errors that occur when the data being processed is hit with a noise phenomenon, typically when the data is on a data bus. The computer tries to interpret the noise as a data bit, which can cause errors in addressing or processing program code. The bad data bit can even be saved in memory and cause problems at a later time.
With the increased layout density in VLSI chips, crosstalk and ground bounce are becoming more common place occurrences. Soft errors on non-data flow (“control”) circuits are particularly difficult to detect. Several methods exist for detecting soft errors in data flow circuits, such as adding bits for parity and error correcting code. However, these are not practical solutions for control circuits, as control circuits require in-depth knowledge of seemingly unrelated control logic cones.
Therefore, it would be advantageous to have an improved method and apparatus for soft error detection in control circuits.